B cell-mediated antibody responses are an essential component of immunity and the main target of vaccine development. B cell signaling activation is triggered by the binding of B cell receptors (BCR) with antigen displayed on the surface of professional antigen presenting cells. Although soluble antigen are able to activate B cells, recent studies have shown that surface anchored antigens are significantly more efficient in triggering B cell activation. Consequently, the physical nature of antigen presentation and the mechanical environment of B cells are likely important for BCR activation. In particular, B cells encounter antigen on APC, which possess complex surfaces with convoluted topographies, a fluid membrane and deformable cell bodies. Historically, planar substrates have been used to study immune cell signaling and investigate the mechanisms behind signal initiation. Previous work has shown that many behaviors of adherent and stem cells, such as morphology, movement and differentiation, are modulated by surface topography. These studies demonstrate that cells are able to respond to topographical cues, which in turn influences cell signaling. However, the question of topographical modulation of signaling in immune cells has not been previously studied. Our preliminary studies suggest that B cell signaling and actin dynamics are both influenced by the nanotopography of the antigen-presenting surface. The central hypothesis of this project is that substrate topography influences B signaling and activation. Furthermore, cytoskeletal dynamics at the interface enable the cell to sense topography in order to generate an appropriate signaling response. We will test this hypothesis by using novel nanotopographic surfaces that allow high resolution fluorescence imaging to examine actin cytoskeletal dynamics, BCR signaling and actin regulators in B cells. Aim 1 will examine the effects of substrate nanotopography on B-cell morphology, actin reorganization and signaling activation. We will use nonlinear optical lithography to fabricate novel surfaces with nanotopographic patterns on materials that permit high-resolution live cell imaging of the cell-substrate interface. Using these substrates, we will establish that substrate topography is an important modulator of B cell signaling and cytoskeletal dynamics. Aim 2 will define actin remodeling and their upstream regulators that are critical for topography sensing and the control of BCR signaling. To do so, we will perturb the actomyosin cytoskeleton using small-molecule inhibitors and gene knockout of regulatory proteins including WASP and N-WASP in modulating topographic sensing in B cells via actin remodeling. We will further test the role of curvature sensing proteins in topographic sensing by the control of membrane curvature. These studies will provide important new insights into how actin regulatory pathways mediate topographic sensing, giving us another means of tuning B cell signaling with nanotopography. More broadly, this work will shed light on mechanisms by which cells sense their environment by surface receptors, which has considerable implications for biomedicine.